1. Field of the Invention
The invention relates to compositions used in the manufacture of vehicle body panels, and particularly to panels which require a high degree of energy absorption. An example of such a panel is the dashboard or instrument panel of an automotive vehicle which is required to perform an energy absorbing function when struck during an accident. Complete shattering of such a panel with slight energy absorption and no rebound could be dangerous. On the other hand, extreme rebound characteristics with very little energy absorption could also be extremely harmful, if for example, is is struck by a human head.
2. Description of the Prior Art
A search revealed the follwoing patents relating to structural plastic materials designed to exhibit specific properties when impacted, but which utilize fiber glass and do not incorporate the materials of the present invention: Davies et al 2,873,226 February 10, 1959 Walker et al 2,881,110 April 7, 1959 Walker 2,938,737 May 31, 1960 Johnston 3,113,788 December 10, 1963 Goerden et al 3,536,549 October 27, 1970 Andersen 3,573,144 March 30, 1971 March, Jr. et al 3,642,560 February 15, 1972 Woodham et al 3,655,850 April 11, 1972
A conventional automotive grade premix, whether made with general purpose polyester resins or low shrink resins and reinforced with sisal or sisal in combination with small amounts of glass fibers, has low impact strength and little energy absorption in the usual thicknesses in which heater housings, consoles, door panel foundations and conceivably instrument panel foundations would be made.
As an example and for purposes of illustration if an edge supported flat panel size 1/10 .times. 12 .times. 12 inches made from a sisal reinforced premix is impacted with a 4 lb. ball falling freely 6 ft., the panel will shatter into two or more pieces with the ball instantaneously passing through the panel with very slight energy absorption and obviously no rebound. The behavior is very analogous to what would happen if a piece of ordinary window glass were so impacted. Such a sisal reinforced compound is typified by formulation A. Izod properties are also stated.
______________________________________ FORMULATION A A low shrink sisal reinforced Premix compound COMPONENT % Wt. ______________________________________ Paraplex P-340 Resin (Rohm & Haas Co.) 12.00 Paraplex P-701 Thermoplastic Additive 6.54 Benzoyl Peroxide (55% Paste) .16 Tert-butyl Perbenzoate .08 Inhibitor .06 Calcium Carbonate (Camel-carb) 65.48 Clay (ASP-200) 6.45 Calcium Stearate 1.81 Sisal, chopped 3/8" long 7.42 100.00 Izod Impact Strength: 1.20 Ft. Lbs./inch of Notch ______________________________________
At the other extreme, for example, is a sheet molding compound (SMC) made with a low shrink polyester resin and a considerable amount of long glass fibers as reinforcement. Such material is commonly used to mold truck fenders, fender extensions, front end pieces, etc. for automobiles.
If an edge supported 1/10 .times. 12 .times. 12 panel of this material is impacted in the same manner, i.e., 4 lb. ball 6 ft., the panel will not shatter; in fact, only a small area the size of a quarter on the reverse side of the panel receiving the blow will show some fiber disruption. However, and importantly, the ball will obviously not penetrate through the panel but will rebound a considerable distance, indicating very little energy absorption, i.e., very little deceleration of the ball, but rather an instantaneous reversal in direction. With a human head a high G-force would no doubt result with probable skull fracture or concussion. The behavior is very analogous to what would happen with a steel panel.
Such a SMC compound is typified by formulation B with Izod properties also shown.
______________________________________ FORMULATION B A low shrink, high strength, SMC compound COMPONENT % Wt. ______________________________________ Paraplex P-340 16.20 Paraplex P-701 10.80 Tert-butyl Perbenzoate .30 Calcium Carbonate 40.50 Mg (OH) Thickener .70 Zinc Stearate 1.50 2" Chopped Fiber glass 30.00 100.00 Izod Impact Strength: 15.0 Ft. Lbs. /inch of Notch ______________________________________
Polyester premix molding compounds are well extablished in the trade and are used to mold many different articles. Such compounds are most usually composed of an unsaturated polyester resin in a reactive monomer, suitable inhibitors for maintaining practical shelf life prior to molding, free radical generating catalysts to initiate resin reaction during molding, a suitable filler system, a lubricant to provide release from the mold, a colorant and reinforcing fibers. The preparation of these resins, types of raw materials and methods of preparing premix compounds have been well described in technical literature, including patents such as U.S. Pat. Nos. 2,255,313; 2,632,751; 3,227,665 and 3,701,748. The latter describes a suitable type of low shrinkage resin system for the present invention. U.S. Pat. No. 3,227,665, while directed to other subject matter, mentions various types of inorganic and organic reinforcing fibers in a polymerizable, cross-linkable unsaturated polyester resin composition.